Method, device and program for coding and decoding acoustic parameter, and method, device and program for coding and decoding sound

ABSTRACT

In coding and decoding an acoustic parameter, a weighted vector is generated by multiplying a code vector output in a past frame and a code vector selected in a present frame by weighting factors respectively selected from a factor code book and adding the products to each other.

TECHNICAL FIELD

This invention relates to methods of coding and decoding low-bit rateacoustic signals in the mobile communication system and Internet whereinacoustic signals, such as speech signals and music signals, are encodedand transmitted, and also relates to acoustic parameter coding anddecoding methods and devices applied thereto, and programs forconducting these methods by a computer.

PRIOR ART

In the fields of digital mobile communication and speech storage, inorder to effectively utilize radio waves and storage media, there havebeen used speech coding devices wherein the speech information iscompressed and encoded with high efficiency. In these speech codingdevices, in order to express the high-quality speech signals even at thelow bit rate, there has been employed a system using a model suitablefor expressing the speech signals. As a system which has been widely inactual use at the bit rates in the range of 4 kbit/s to 8 kbit/s, forexample, CELP (Code Excited Linear Prediction: Code Excited LinearPrediction Coding) system can be named. The art of CELP has beendisclosed in M. R. Schroeder and B. S. Atal: “Code-Excited LinearPrediction (CELP): High-quality Speech at Very Low Bit Rates”, Proc.ICASSP-85, 25.1.1, pp.937–940, 1985”.

The CELP type speech coding system is based on a speech synthetic modelcorresponding to a vocal tract mechanism of human being, and a filterexpressed by a linear predictive coefficient indicating a vocal tractcharacteristics and an excitation signal for driving the filtersynthesize the speech signal. More particularly, a digitalized speechsignal is delimited by every certain length of a frame (about 5 ms to 50ms) to carry out the linear prediction of the speech signal for everyframe, so that a predicted residual error (excitation signal) is encodedby using an adaptive code vector formed of a known waveform and a fixedcode vector. The adaptive code vector is stored in an adaptive codebookas a vector which expresses a driving sound source signal generated inthe past, and is used for expressing periodic components of the speechsignal. The fixed code vector is stored in a fixed codebook as a vectorprepared in advance and having a predetermined number of waveforms, andthe fixed code vector is used for mainly expressing aperiodic componentswhich can not be expressed by the adaptive codebook. As the vectorstored in the fixed codebook, a vector formed of a random noise sequenceand a vector expressed by a combination of several pulses are used.

As a representative example of the fixed codebooks that express thefixed code vectors by the combination of several pulses, there is analgebraic fixed codebook. More specific contents of the algebraic fixedcodebook are shown in “ITU-T Recommendation G. 729” and the like.

In the conventional speech coding system, the linear predictivecoefficients of the speech are converted into parameters, such aspartial autocorrelation (PARCOR) coefficients and line spectrum pairs(LSP: Line Spectrum Pairs, also called as line spectrum frequencies),and quantized further to be converted into the digital codes, and thenthey are stored or transmitted. The details of these methods aredescribed in “Digital Speech Processing” (Tokai University Press)written by Sadaoki Furui, for example.

In the coding of the linear predictive coefficients, as a method ofcoding the LSP parameter, a quantized parameter of the current frame isexpressed by a weighted vector in which a code vector outputted from thevector codebook in a one or more frames in the past is multiplied by aweighting coefficient selected from a weighting coefficient codebook, ora vector in which a mean vector, found in advance, of the LSP parameterin the entire speech signal is added to this vector, and a code vectorwhich should be outputted by the vector codebook and a set of weightingcoefficients that should be outputted by the weighting coefficientcodebook are selected such that a distortion with respect to the LSPparameter found from an input speech in the quantized parameter, thatis, the quantization distortion becomes minimum or small enough. Then,they are outputted as codes of the LSP parameter.

This is generally called a weighted vector quantization, or supposingthat the weighting coefficients are considered as the predictivecoefficients from the past, it is called a moving average (MA: MovingAverage) prediction vector quantization.

In a decoding side, from the received vector code and the weightingcoefficient code, the code vector in the current frame and the past codevector are multiplied by the weighting coefficient, or, a vector, inwhich the mean vector, found in advance, of the LSP parameter in theentire speech signal is added further, is outputted as a quantizedvector in the current frame.

As a vector codebook that outputs the code vector in each frame, therecan be structured a basic one-stage vector quantizer, a split vectorquantizer wherein dimensions of the vector are divided, a multi stagevector quantizer having two or more stages, or a multi-stage and splitvector quantizer in which the multi stage vector quantizer and the splitvector quantizer are combined.

In the aforementioned conventional LSP parameter encoder and decoder,since the number of frames is large in a silent interval and astationary noise interval, and in addition, since the coding process anddecoding process are configured in multi stages, it was not alwayspossible to output the vector such that the parameter synthesized incorrespondence with the silent interval and the stationary noiseinterval can be changed smoothly. This is because of the followingreasons. Normally, the vector codebook used for coding was found bylearning, but since learned speeches did not contain enough amount ofthe silent interval or the stationary noise interval upon this learning,the vector corresponding to the silent interval or the stationary noiseinterval was not always reflected enough to learn, or if the number ofbits given to the quantizer was small, it was impossible to design thecodebook including sufficient quantized vectors corresponding tonon-voice intervals.

In these LSP parameter encoder and decoder, upon coding at the time ofactual communication, the quantization performance during the non-voiceinterval could not be fully exhibited, and a deterioration of thequality as the reproduced sound was inevitable. Also, these problemsoccurred not only in the coding of the acoustic parameter equivalent tothe linear predictive coefficient expressing a spectrum envelope of thespeech signal, but also in the similar coding with respect to a musicsignal.

The present invention has been made in view of the foregoing points, andan object of the invention is to provide acoustic parameter coding anddecoding methods and devices, wherein outputting the vectors equivalentto the silent interval and the stationary noise interval is facilitatedso that the deterioration of the quality is scarce at these intervals inthe conventional coding and decoding of the acoustic parameterequivalent to the linear predictive coefficient expressing a spectrumenvelope of the acoustic signal, and also to provide acoustic signalcoding and decoding methods and devices using the aforementioned methodsand devices, and a program for conducting these methods by a computer.

DISCLOSURE OF THE INVENTION

The present invention is mainly characterized in that in coding anddecoding of an acoustic parameter equivalent to a linear predictivecoefficient showing a spectrum envelope of an acoustic signal, that is,a parameter such as an LSP parameter, α parameter, PARCOR parameter orthe like (hereinafter simply referred to as an acoustic parameter), anacoustic parameter vector code a substantially flat spectrum envelopecorresponding to a silent interval or stationary noise interval, whichcan not originally obtained by learning by a Codebook, and added to avector codebook, to thereby be selectable. The present invention isdifferent from the prior art in that a vector including a component ofthe acoustic parameter vector showing the substantially flat spectrumenvelope is obtained in advance by calculation and stored as one of thevectors of the vector codebook, and in a multi-stage quantizationconfiguration and a split vector quantization configuration, theaforementioned code vector is outputted.

An acoustic parameter coding method according to the present inventioncomprises:

(a) a step of calculating an acoustic parameter equivalent to a linearpredictive coefficient showing a spectrum envelope characteristic of anacoustic signal for every frame of a predetermined length of time;

(b) a step of multiplying a code vector outputted in at least one framein the closest past selected from a vector codebook for storing aplurality of code vectors in correspondence with an index representingthe code vectors and a code vector selected in a current framerespectively with a set of weighting coefficients selected from acoefficient codebook for storing one or more sets of weightingcoefficients in correspondence with an index representing the weightingcoefficients, wherein multiplied results are added to generate aweighted vector and a vector including a component of the weightedvector is found as a candidate of a quantized acoustic parameter withrespect to the acoustic parameter of the current frame; and

(c) a step of determining the code vector of the vector codebook and theset of the weighting coefficients of the coefficient codebook by using acriterion such that a distortion of the candidate of the quantizedacoustic parameter with respect to the calculated acoustic parameterbecomes a minimum, wherein an index showing the determined code vectorand the determined set of the weighting coefficients are determined andoutputted as a quantized code of the acoustic parameter; and

the vector codebook includes a vector having a component of an acousticparameter vector showing the aforementioned substantially flat spectrumenvelope as one of the stored code vectors.

An acoustic parameter decoding method according to the present inventioncomprises:

(a) a step of outputting a code vector corresponding to an indexexpressed by a code inputted for every frame and a set of weightingcoefficients from a vector codebook, which stores a plurality of codevectors of an acoustic parameter equivalent to a linear predictivecoefficient showing a spectrum envelope characteristic of an acousticsignal in correspondence with an index representing the code vectors,and a coefficient codebook, which stores one or more sets of weightingcoefficients in correspondence with an index representing the sets; and

(b) a step of multiplying the code vector outputted from the vectorcodebook in at least one frame of the closest past and a code vectoroutputted from the vector codebook in a current frame respectively withthe outputted set of the weighting coefficients, and adding multipliedresults together to thereby generate a weighted vector, wherein a vectorincluding a component of the weighted vector is outputted as a decodedquantized vector of the current frame; and

the vector codebook includes a vector having a component of an acousticparameter vector showing a substantially flat spectrum envelope as oneof the code vectors stored therein.

An acoustic parameter coding device according to the present inventioncomprises:

parameter calculating means for analyzing an input acoustic signal forevery frame and calculating an acoustic parameter equivalent to a linearpredictive coefficient showing a spectrum envelope characteristic of theacoustic signal;

a vector codebook for storing a plurality of code vectors incorrespondence with an index representing the vectors;

a coefficient codebook for storing one or more sets of weightingcoefficients in correspondence with an index representing thecoefficients;

quantized parameter generating means for multiplying a code vector withrespect to a current frame outputted from the vector codebook and a codevector outputted in at least one frame of the closest past respectivelywith the set of the weighting coefficients selected from the coefficientcodebook, the quantized parameter generating means adding resultstogether to thereby generate a weighted vector, the quantized parametergenerating means outputting a vector including a component of thegenerated weighted vector as a candidate of a quantized acousticparameter with respect to the acoustic parameter in the current frame;

a distortion computing part for computing a distortion of the quantizedacoustic parameter with respect to the acoustic parameter calculated atthe parameter calculating means; and

it is configured that a codebook search controlling part for determiningthe code vector of the vector codebook and the set of the weighingcoefficients of the coefficient codebook by using a criterion such thatthe distortion becomes small, the codebook search controlling partoutputting indexes respectively representing the determined code vectorand the set of the weighting coefficients as codes of the acousticparameter; and

the vector codebook includes a vector having a component of an acousticparameter vector showing a substantially flat spectrum envelope.

An acoustic parameter decoding device according to the present inventionis configured to comprise:

a vector codebook for storing a plurality of code vectors of an acousticparameter equivalent to a linear predictive coefficient showing aspectrum envelope characteristic of an acoustic signal in correspondencewith an index representing the code vectors,

a coefficient codebook for storing one or more sets of weightingcoefficients in correspondence with an index representing the weightingcoefficients, and

quantized parameter generating means for outputting one code vector fromthe vector codebook in correspondence with an index showing a codeinputted for every frame, to thereby output a set of weightingcoefficients from the coefficient codebook, the quantized parametergenerating means multiplying the code vector outputted in a currentframe and a code vector outputted in at least one frame of the closestpast respectively with the set of the weighting coefficients outputtedin the current frame, the quantized parameter generating means addingmultiplied results together to thereby generate a weighted vector andoutputting a vector including a component of the generated weightedvector as a decoded quantized acoustic parameter of the current frame;and

the vector codebook stores a vector including a component of an acousticparameter showing a substantially flat spectrum envelope as one of thecode vectors.

An acoustic signal coding device for encoding an input acoustic signalaccording to the present invention is configured to comprise:

means for encoding a spectrum characteristic of an input acoustic signalby using the aforementioned acoustic parameter coding method;

an adaptive codebook for holding adaptive code vectors showing periodiccomponents of the input acoustic signal therein;

a fixed codebook for storing a plurality of fixed vectors therein;

filtering means for inputting as an excitation signal a sound sourcevector generated based on the adaptive code vector from the adaptivecodebook and the fixed vector from the fixed codebook, the filteringmeans synthesizing a synthesized acoustic signal by using a filtercoefficient based on the quantized acoustic parameter; and

means for determining an adaptive code vector and a fixed code vectorrespectively selected from the adaptive codebook and the fixed codebooksuch that a distortion of the synthesized acoustic signal with respectto the input acoustic signal becomes small, the means outputting anadaptive code and a fixed code respectively corresponding to thedetermined adaptive code vector and the fixed vector.

An acoustic signal decoding device for decoding an input code andoutputting an acoustic signal according to the present invention isconfigured to comprise:

means for decoding an acoustic parameter equivalent to a linearpredictive coefficient showing a spectrum envelope characteristic froman inputted code by using the aforementioned acoustic parameter decodingmethod;

a fixed codebook for storing a plurality of fixed vectors therein;

an adaptive codebook for holding adaptive code vectors showing periodiccomponents of a synthesized acoustic signal therein;

means for taking out a corresponding fixed vector from the fixedcodebook and taking out a corresponding adaptive code vector from theadaptive codebook by an inputted adaptive code and an inputted fixedcode, the means synthesizing the vectors and generating an excitationvector; and

filtering means for setting a filter coefficient based on the acousticparameter and reproducing an acoustic signal by the excitation vector.

An acoustic signal coding method for encoding an input acoustic signalaccording to the present invention comprises:

(A) a step of encoding a spectrum characteristic of an input acousticsignal by using the aforementioned acoustic parameter coding method;

(B) a step of using as an excitation signal a sound source vectorgenerated based on an adaptive code vector from an adaptive codebook forholding adaptive code vectors showing periodic components of an inputacoustic signal therein and a fixed vector from a fixed codebook forstoring a plurality of fixed vectors therein, and carrying out asynthesis filter process by a filter coefficient based on the quantizedacoustic parameter to thereby generate a synthesized acoustic signal;and

(C) a step of determining an adaptive code vector and a fixed vectorselected from the fixed codebook and the adaptive codebook such that adistortion of the synthesized acoustic signal with respect to the inputacoustic signal becomes small, and outputting an adaptive code and afixed code respectively corresponding to the determined adaptive codevector and the fixed vector.

An acoustic signal decoding method for decoding input codes andoutputting an acoustic signal according to the present inventioncomprises:

(A) a step of decoding an acoustic parameter equivalent to a linearpredictive coefficient showing a spectrum envelope characteristic frominputted codes by using the aforementioned acoustic parameter decodingmethod;

(B) a step of taking out an adaptive code vector from an adaptivecodebook for holding therein adaptive code vectors showing periodiccomponents of an input acoustic signal by an inputted adaptive code andan inputted fixed code, taking out a corresponding fixed vector from afixed codebook for storing a plurality of fixed vectors therein, andsynthesizing the adaptive code vector and the fixed vector to therebygenerate an excitation vector; and

(C) a step of carrying out a synthesis filter process of the excitationvector by using a filter coefficient based on the acoustic parameter,and reproducing a synthesized acoustic signal.

The aforementioned invention can be provided in a form of a programwhich can be conducted in the computer.

According to the present invention, in the weighted vector quantizer(or, MA prediction vector quantizer), since a vector including acomponent of an acoustic parameter vector showing a substantially flatspectrum is found and stored as the code vector of the vector codebook,a quantized vector equivalent to the corresponding silent interval orthe stationary noise interval can be outputted.

Also, according to another embodiment of the invention, as aconfiguration of a vector codebook comprised in the acoustic parametercoding device and decoding device, in the case of using a multi-stagevector codebook, a vector including a component of an acoustic parametervector showing a substantially spectrum envelope is stored a codebook ofone stage thereof, and a zero vector is stored in the codebooks of theother stages. Accordingly, an acoustic parameter equivalent to acorresponding silent interval or stationary noise interval can beoutputted.

It is not always necessary to store the zero vector. In the case of notstoring the zero vector, when the vector including the component of theacoustic parameter vector showing the substantially flat spectrumenvelope from a codebook of one stage is selected, it will suffice thatthe vector including the component of the acoustic parameter vectorshowing the substantially flat spectrum envelope is outputted as acandidate of the code vector of the current frame.

Also, in the case that the vector codebook is formed of a split vectorcodebook, there are used a plurality of split vectors in whichdimensions of vectors including a component of an acoustic parametervector showing a substantially flat spectrum envelope are divided, andby divisionally storing these split vectors one by one in a plurality ofsplit vector codebooks, respectively, when searching in the respectivesplit vector codebooks, the respective split vectors are selected, and avector by integrating these split vectors can be outputted as aquantized vector equivalent to the corresponding silent interval or thestationary noise interval.

Furthermore, the vector quantizer may be formed to have the multi-stageand split quantization configuration, and by combining the arts of theaforementioned multi-stage vector quantization configuration and thesplit vector quantization configuration, there can be outputted as thequantized vector equivalent to the acoustic parameter in correspondencewith the corresponding silent interval or the stationary noise interval.

In the case that the codebook is structured as the multi-stageconfiguration, in correspondence with respective code vectors of thecodebook at the first stage, scaling coefficients respectivelycorresponding to the codebooks on and after the second stage areprovided as the scaling coefficient codebook. The scaling coefficientscorresponding to the code vector selected at the codebook of the firststage are read out from the respective scaling coefficient codebooks,and multiplied with code vectors respectively selected from the codebookof the second stage, so that the coding with much smaller distortion ofthe quantization can be achieved.

As described above, the acoustic parameter coding and decoding methodsand the devices in which the quality deterioration is scarce in theaforementioned interval, that is, the object of the invention, can beprovided.

In the acoustic signal coding device of the invention, in thequantization of the linear predictive coefficient, any one of theaforementioned parameter coding devices is used in an acoustic parameterarea equivalent to the linear predictive coefficient. According to thisconfiguration, the same operation and effects as those of theaforementioned one can be obtained.

In the acoustic signal decoding device of the invention, in decoding ofthe linear predictive coefficient, any one of the aforementionedparameter coding devices is used in the acoustic parameter areaequivalent to the linear predictive coefficient. According to thisconfiguration, the same operation and effects as those of theaforementioned one can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a functional configuration of anacoustic parameter coding device to which a codebook according to thepresent invention is applied.

FIG. 2 is a block diagram showing a functional configuration of anacoustic parameter decoding device to which a codebook according to thepresent invention is applied.

FIG. 3 is a diagram showing an example of a configuration of a vectorcodebook according to the present invention for LSP parameter coding anddecoding.

FIG. 4 is a diagram showing an example of a configuration of a vectorcodebook according to the present invention in case of a multi stagestructure.

FIG. 5 is a diagram showing an example of a configuration of a vectorcodebook according to the present invention in the case that a scalingcoefficient is adopted in the multi stage vector codebook.

FIG. 6 is a diagram showing an example of a configuration of vectorcodebook according to the present invention in the case of being formedof a split vector codebook.

FIG. 7 is a diagram showing an example of a configuration of a vectorcodebook according to the present invention in the case that a secondstage codebook is formed of the split vector codebook.

FIG. 8 is a diagram showing an example of a configuration of a vectorcodebook in the case that scaling coefficients are respectively adoptedin two split vector codebooks in the codebook of FIG. 7.

FIG. 9 is a diagram showing an example of a configuration of a vectorcodebook in the case that each stage in the multi stage codebook of FIG.4 is structured as the split vector codebook.

FIG. 10A is a block diagram showing an example of a configuration of aspeech signal transmission device to which the coding method accordingto the present invention is applied.

FIG. 10B is a block diagram showing an example of a configuration of aspeech signal receiving device to which the decoding method according tothe present invention is applied.

FIG. 11 is a diagram showing a functional configuration of a speechsignal coding device to which the coding method according to the presentinvention is applied.

FIG. 12 is a diagram showing a functional configuration of a speechsignal decoding device to which the decoding method according to thepresent invention is applied.

FIG. 13 is a diagram showing an example of a configuration in the casethat the coding device and the decoding device according to the presentinvention are put into operation by a computer.

FIG. 14 is a graph for explaining effects of the present invention.

THE BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

Next, embodiments of the invention will be explained with reference tothe drawings.

FIG. 1 is a block diagram showing an example of a configuration of anembodiment of an acoustic parameter coding device to which a linearpredictive parameter coding method according to the present invention.The coding device is formed of a linear prediction analysis part 12; anLSP parameter calculating part 13; and a codebook 14, a quantizedparameter generating part 15, a distortion computing part 16, and acodebook search control part 17, which form a parameter coding part 10.In the figure, a series of digitalized speech signal samples, forexample, are inputted from an input terminal T1. In the linearprediction analysis part 12, the speech signal sample of every one framestored in an internal buffer is subjected to the linear predictionanalysis, to calculate a pair of linear predictive coefficients. Now,supposing the order of the linear prediction analysis is p-dimension,the p-dimensional, equivalent LSP (line spectrum pairs) parameter iscalculated from the p-dimensional linear predictive coefficient in theLSP parameter calculating part 13. The details of the processing methodthereof were described in the literature written by Furui mentionedabove. The p LSP parameters are expressed as vectors as follows.f(n)=(f ₁(n), f ₂(n), . . . , f _(p)(n))  (1)Here, the integer n indicates a certain frame number n, and hereinafter,the frame of this number is referred to as a frame n.

The codebook 14 is provided with a vector codebook 14A, which stores ncode vectors representing LSP parameter vectors found by learning, and acoefficient codebook 14B which stores a set of K weighting coefficients,and by an index Ix(n) for specifying the code vector and an index Iw(n)for specifying the weighting coefficient code, a corresponding codevector x(n) and a set of weighting coefficients (w₀, w₁, . . . , w_(m))are outputted. The quantized parameter generating part 15 is formed of mpieces of buffer parts 15B₁, . . . , 15B_(m), which are connected inseries; m+1 pieces of multipliers 15A₀, 15A₁, . . . , 15A_(m), aregister 15C, and a vector adder 15D. The code vector x(n) in thecurrent frame n which is selected as one of the candidates from thevector codebook 14A and code vectors x(n−1), . . . , x(n−m) which aredetermined with respect to the past frame n−1, . . . , n−m arerespectively multiplied by a set of the selected weighting coefficientsw₀, . . . , w_(m) at the multipliers 15A₀, 15A_(m), and the results ofmultiplications are added together at the adder 15D. Further, a meanvector y_(ave), found in advance, of the LSP parameter in the entirespeech signal is added to the adder 15D from the register 15C. Asdescribed above, from the adder 15D, a candidate of the quantizedvector, that is, a candidate y(n) of the LSP parameter, is generated. Asthe mean vector y_(ave), a mean vector at a voice part may be used, or azero vector may be used as described later.

When the code vector x(n) selected from the vector codebook 14A withrespect to the current frame n is substituted asx(n)=(x ₁(n), x ₂(n), . . . , x _(p)(n))  (2)and then, similarly, the code vector determined one frame before issubstituted as x(n−1); the code vector determined two frame before issubstituted as x(n−2); and the code vector determined m frame before issubstituted as x(n−m); a quantized vector candidate of the currentframe, that is,y(n)=(y ₁(n), y ₂(n), . . . , y _(p)(n))  (3)is expressed as follows:y(n)=w ₀ ·x(n)+Σ_(j=1) ^(m) w _(j) ·x(n−j)+y _(ave)  (4)Here, the larger a value of m is, the better the quantization efficiencyis. However, the effect at the occurrence of a code error extends toportions after the m frame, and in addition, in case the coded andstored speech is reproduced from the middle thereof, it is necessary togo back to the m frame past. Therefore, m is adequately selected asoccasion demands. For speech communication, in case of the one frame 20ms, the value of m is sufficient if it is 6 or more, and even the value1 to 3 may suffice. The number m is also called as the order of themoving average prediction.

The candidate y(n) of the quantization obtained as described above issent to the distortion computing part 16, and the quantizationdistortion with respect to the LSP parameter f(n) calculated at the LSPparameter calculating part 13 is computed. The distortion d is definedby the weighted Euclidean distance as follows.d=Σ _(i=1) ^(p) r _(i)(f _(i)(n)−y _(i)(n))²  (5)Incidentally, r_(i), i=1, . . . , p are weighting coefficients found bythe LSP parameter f(n), and if they are set to the weighting so as tostress on and around the formant frequency of the spectrum, theperformance becomes excellent.

In the codebook search control part 17, pairs of the indexes Ix(n) andIw(n) given to the codebook 14 are sequentially changed, and thecalculation of the distortion d by the equation (5) as described aboveare repeated with regard to the respective pairs of the indexes, so thatfrom the code vector of the vector codebook 14A and the set of theweighting coefficients of the vector codebook 14A in the codebook 14,the one pair thereof making the distortion d as the output from thedistortion computing part 16 to be the smallest or small enough issearched, and these indexes Ix(n) and Iw(n) are sent out as the codes ofthe input LSP parameter from a terminal T2. The codes Ix(n) and Iw(n)sent out from the terminal T2 are sent to a decoder via a transmissionchannel, or stored in a memory.

When the output code vector x(n) of the current frame is determined, thecode vectors x(n−j), j=1, . . . , m−1 in the buffer part 15B_(j) of thepast frame (n−j) are sequentially sent to the next buffer part15B_(j+1), and the code vector x(n) of the current frame n is inputtedinto the buffer 15B₁.

The invention is characterized in that as one of the code vectors storedthe vector codebook 14A used in the coding by the weighted vectorquantization of the LSP parameter described above or the moving averagevector quantization, in case the mean vector y_(ave) is zero, the LSPparameter vector F corresponding to the silent interval or stationarynoise interval is stored, or in case y_(ave) is not zero, a vector C₀found by subtracting y_(ave) from the LSP parameter vector F is stored.Namely, in case y_(ave) is not zero, the LSP parameter vectorcorresponding to the silent interval or the stationary noise intervalconstitutes:F=(F_(1,)F2, . . . , F_(p))  (6)and the code vector C₀ which should be stored in the vector codebook 14Ain FIG. 1 is calculated as follows:C ₀ F−y _(ave)  (7)In the coding by the moving average prediction at the silent interval orthe stationary noise interval, when the C₀ is selected consecutivelythroughout m frames, the quantized vector y(n) is found as follows:

$\begin{matrix}\begin{matrix}{{y(n)} = {{w_{0} \cdot {x(n)}} + {\sum\limits_{j = 1}^{m}\;{w_{j} \cdot {x\left( {n - j} \right)}}} + y_{ave}}} \\{= {{w_{0} \cdot C_{0}} + {\sum\limits_{j = 1}^{m}\;{w_{j} \cdot C_{0}}} + y_{ave}}} \\{= {{\left( {w_{0}{\sum\limits_{j = 1}^{m}\; w_{j}}} \right) \cdot C_{0}} + y_{ave}}}\end{matrix} & (8)\end{matrix}$Here, supposing that the sum of the weighting coefficients from w₀ tow_(m) is 1 or the value close thereto, y(n) can be outputted as thequantized vector F found from the LSP parameter at the silent intervalor the vector close thereto, so that the coding performance at thesilent interval or the stationary noise interval can be improved. By theconfiguration as described above, the vector including the component ofthe vector F is stored as one of the code vectors in the vector codebook14A. As the code vector including the component of the vector F, in casethe quantized parameter generating part 15 generates the quantizedvector y(n) including the component of the mean vector y_(ave), the onefound by subtracting the mean vector y_(ave) from the vector F is used,and in case quantized parameter generating part 15 generates thequantized vector y(n) that does not include the component of the meanvector y_(ave), the vector F itself is used.

FIG. 2 is an example of a configuration of a decoding device to which anembodiment of the invention is applied, and the decoding device isformed of a codebook 24 and a quantized parameter generating part 25.These codebook 24 and the quantized parameter generating part 25 arestructured respectively similarly to the codebook 14 and the quantizedparameter generating part 15 in FIG. 1. The indexes Ix(n) and Iw(n) asthe parameter codes sent from the coding device of FIG. 1 are inputted,and the code vector x(n) corresponding to the index Ix(n) is outputtedfrom the vector codebook 24A, and the set of weighting coefficients w₀,w₁, . . . , w_(m) corresponding to the index Iw(n) are outputted fromthe coefficient codebook 24B. The code vector x(n) respectivelyoutputted per frame from the vector codebook 24A is sequentiallyinputted into buffer parts 25B₁, . . . , 25B_(m), which are connected inseries. The code vector x(n) of the current frame n and code vectorsx(n−1), . . . , x(n−m) at 1, . . . , m frame past of the buffer parts25B₁, . . . , 25B_(m) are multiplied by weighting coefficients w₀, w₁, .. . , w_(m), in multipliers 25A₀, 25A₁, . . . , 25A_(m), and thesemultiplied results are added together at adder 25D. Further, a meanvector y_(ave) of the LSP parameter in the entire speech signal, whichis held in advance in a register 25C, is added to the adder 25D, and theaccordingly obtained quantized vector y(n) is outputted as a decodingLSP parameter. The vector y_(ave) can be the mean vector of the voicepart, or can be a zero vector z.

In the present invention, also in the decoding device, as in the codingdevice shown in FIG. 1, by storing the vector C₀ as one of the codevectors in the vector codebook 24A, the LSP parameter vector F found atthe silent interval or the stationary noise interval of the acousticsignal can be outputted.

In case the mean vector y_(ave) is not added at the adder 15D in FIG. 1and at the adder 25D in FIG. 2, the LSP parameter vector F correspondingto the silent interval and the stationary noise interval is storedinstead of the vector C₀ in the vector codebooks 14A and 24A. In thefollowing explanations, the LSP parameter vector F or vector C₀ storedin the respective vector codebooks 14A and 24A are represented by andreferred to as the vector C₀.

In FIG. 3, an example of a configuration of the vector codebook 14A inFIG. 1, or the vector codebook 24A is shown as a vector codebook 4A.This example is the one in case one-stage vector codebook 41 is used. Npieces of code vectors x₁, . . . , x_(N) are stored as they are in thevector codebook 41, and corresponding to the inputted index Ix(n), anyone of the N code vectors is selected and outputted. In the presentinvention, as one of the code vector x, the code vector C₀ is used.Although N code vectors in the vector codebook 41 is formed by learningas in the conventional one, for example, in the present invention, onevector, that is most similar (distortion is small) to the vector C₀among these vectors, is substituted by C₀, or C₀ is simply added.

There are several methods for finding the vector C₀. As one of them,since the spectrum envelope of the input acoustic signal normallybecomes flat at the silent interval or the stationary noise interval, inthe case of p-dimensional LSP parameter vector F, for example, 0 to πare divided equally by p+1, and p values having the substantially equalinterval in size, such as π/(1+p), 2π/(1+p), . . . , π/(1+p), may beused as the LSP parameter vector. Alternatively, from the actual LSPparameter vector F at the silent interval and the stationary noiseinterval, it can be found by C₀=F−y_(ave). Or, the LSP parameter in thecase of inputting the white noise or Hoth noise may be used as theparameter vector F, to find C₀=F−y_(ave). Incidentally, in general, themean vector y_(ave) of the LSP parameter among the entire speech signalis found as a mean vector of all of the vectors for learning when thecode vector x of the vector codebook 41 is learned.

The following Table 1 show examples of the ten-dimensional vectors C ⁰ ,y _(ave), and F wherein the LSP parameters at the silent interval or thestationary noise interval are normalized between 0 to π when p=10dimensional LSP parameters are used as the acoustic parameters.

TABLE 1 p C₀ y_(ave) F 1 0.0498613038 0.250504841 0.300366 2 0.1969140870.376541460 0.573456 3 0.274116971 0.605215652 0.879333 4 0.2224660320.923759106 1.146225 5 0.192227464 1.24066692 1.432894 6 0.1704976241.54336668 1.713864 7 0.139565958 1.85979861 1.999365 8 0.1776384422.10739425 2.285031 9 0.165183997 2.40568568 2.570870 10 0.2505048412.68495222 2.856472

The vector F is the example of the code vector of the LSP parameterrepresenting the silent interval and the stationary noise intervalwritten into the codebook according to the present invention. Values ofthe elements of this vector are increased at substantially constantinterval, and this means that the frequency spectrum is substantiallyflat.

Second Embodiment

FIG. 4 shows another example of the configuration of the vector codebook14A of the LSP parameter encoder of FIG. 1 or the vector codebook 24A ofthe LSP parameter decoding device of FIG. 2, shown as a codebook 4A incase two-stage vector codebook is used. A first-stage codebook 41 storesN pieces of p-dimensional code vectors x₁₁, . . . , x_(1N), and asecond-stage codebook 42 stores N′ pieces of p-dimensional code vectorsx₂₁, . . . , x_(2N′).

Firstly, when the index Ix(n) specifying the code vector is inputted,the index Ix(n) is analyzed at a code analysis part 43, to therebyobtain an index Ix(n)₁ specifying the code vector at the first stage andan index Ix(n)₂ specifying the code vector at the second stage. Then,i-th and i′-th code vectors x_(1i) and x_(2i′) respectivelycorresponding to the indexes Ix(n)₁ and Ix(n)₂ of the respective stagesare read out from the first-stage codebook 41 and the second-stagecodebook 42, and the code vectors are added together at an adding part44, to thereby output the added result as a code vector x(n).

In the case of the two-stage structure vector codebook, the code vectorsearch is carried out by using only the first-stage codebook 41 for apredetermined number of candidate code vectors sequentially startingfrom the one having the smallest quantization distortion. This search isconducted by a combination with the set of the weighting coefficients ofthe coefficients codebook 14B shown in FIG. 1. Then, regarding thecombinations of the first-stage code vectors as the respectivecandidates and the respective code vectors of the second-stage codebook,there is searched a combination of the code vectors in which thequantization distortion is the smallest.

In case the code vector is searched by prioritizing the first-stagecodebook 41 as described above, the code vector C₀ (or F) is prestoredas one of the code vectors in the first-stage codebook 41 of the multistage vector codebook 4A, as well as the zero vector z is prestored asone of the code vectors in the second stage codebook 42. Accordingly, incase the code vector C₀ is selected from the codebook 41, the zerovector z is selected from the codebook 42. As a result, the presentinvention achieves the structure in which the code vector C₀ in the caseof corresponding to the silent interval or the stationary noise intervalcan be outputted as the output of the codebook 4A from the adder 44. Itmay be structured such that in case the zero vector z is not stored andthe code vector C₀ is selected from the codebook 41, the selection andaddition from the codebook 42 are not conducted.

In case the search is conducted for all of the combinations of therespective code vectors in the first-stage codebook 41 and therespective code vectors in the second-stage codebook, the code vector C₀and the zero vector z may be stored in either of the codebooks as longas they are stored in the separate codebooks from each other. It ishighly possible that the code vector C₀ and the zero vector z areselected at the same time in the silent interval or the stationary noiseinterval, but they may not be always selected simultaneously in relationto the computing error and the like. In the codebooks of the respectivestages, the code vector C₀ or the zero vector z becomes a choice forselection as same as the other code vectors.

The zero vector may not be stored in the second-stage codebook 42. Inthis case, if the vector C₀ is selected from the first-stage codebook41, the selection of the code vector from the second-stage codebook 42is not conducted, and it will suffice that the code C₀ of the codebook41 is outputted as it is from the adder 44.

By forming the codebook 4A by the multi stage codebook as shown in FIG.4, this structure is effectively the same as one in which the codevectors are provided only in the number of combinations of theselectable code vectors, and therefore, as compared with the case formedof single stage codebook only as shown in FIG. 3, there is an advantagethat the size (the total number of the code vectors here) of thecodebook can be reduced. Although FIG. 4 shows the case of theconfiguration formed of the two-stage vector codebooks 41 and 42, incase the number of the stages is 3 or more, it will suffice thatcodebooks only in the number corresponding to the additional stages maybe added, and the code vectors are selected from the respectivecodebooks by indexes corresponding to the respective stages, to therebycarry out the vector synthesis of these vectors. Thus, it can be easilyexpanded.

Third Embodiment

FIG. 5 shows the case that in the vector codebook of the embodiment ofFIG. 4, with respect to each code vector of the first-stage codebook 41,a predetermined scaling coefficient is multiplied by the code vectorselected from the second-stage codebook 42, and the multiplied result isadded to the code vector from the first-stage codebook 41 to beoutputted. A scaling coefficient codebook 45 is provided to storescaling coefficients S₁, . . . , S_(N), for example, in the range ofabout 0.5 to 2, determined by learning in advance in correspondence tothe respective vectors x₁₁, . . . , C₀, . . . , x_(1N), and accessed byan index Ix(n)₁ common with the first-stage codebook 41.

Firstly, when the index Ix(n) specifying the code index is inputted, theindex Ix(n) is analyzed at the code analysis part 43, so that the indexIx(n)₁ specifying the code vector of the first stage and the Ix(n)₂specifying the code vector of the second stage are obtained. The codevector x_(1i) corresponding to Ix(n)₁ is read out from the first-stagecodebook 41. Also, from the scaling coefficient codebook 45, the scalingcoefficient s_(i) corresponding to the read index Ix(n)₁. Next, the codevector x_(2i′) corresponding to the Ix(n)₂ is read out from thesecond-stage codebook 42, and in a multiplier 46, the scalingcoefficient s_(i) is multiplied by the code vector x_(2i′) from thesecond-stage codebook 42. The vector obtained by the multiplication andthe code vector x_(1i) from the first-stage codebook 41 are addedtogether at the adding part 44, and the added result is outputted as thecode vector x(n) from the codebook 4A.

Also, in this embodiment, upon searching the code vector, firstly onlythe first-stage codebook 41 is used to search a predetermined number ofthe candidate code vectors sequentially starting from the one having thesmallest quantization distortion. Then, regarding combinations of therespective candidate code vectors and the respective code vectors of thesecond codebook 42, a combination thereof having the smallestquantization distortion is searched. In this case, with respect to themulti stage vector codebook 4A with the scaling coefficients, the vectorC₀ is prestored as one cod vector in the first-stage codebook 41, andthe zero vector z is prestored as one of the code vectors in thesecond-stage codebook 42 as well. Similarly to the case in FIG. 4, ifthe search is conducted for all of the combinations between the codevectors of two codebooks 41 and 42, the code vector C₀ and the zerovector z may be stored either of the codebooks as long as they arestored in the separate codebooks from each other. Alternatively, as inthe embodiments described previously, the zero vector z may not bestore. In that case, if the code vector C₀ is selected, the selectionand addition from the codebook 42 are not conducted.

As described above, the code vector in case of corresponding to thesilent interval or the stationary noise interval can be outputted.Although it is highly possible that the code vector C₀ and the zerovector z are selected at the same time in the silent interval or thestationary noise interval, they may not be always selectedsimultaneously in relation to the computing error and the like. In thecodebooks of the respective stages, the code vector C₀ or the zerovector z becomes a choice for selection as same as the other codevectors. As in the embodiment of FIG. 5, by using the scalingcoefficient codebook 45, this structure is effectively the same as onein which the second-stage codebook is provided only in the number N ofthe scaling coefficients, and therefore, there is an advantage that thecoding with much smaller quantization distortion can be achieved.

Fourth Embodiment

FIG. 6 is a case wherein the vector codebook 14A of the parameter codingdevice of FIG. 1 or the vector codebook 24A of the parameter decodingdevice of FIG. 2 are formed as a split vector codebook 4A, to which thepresent invention is applied. Although the codebook of FIG. 6 is formedof half-split vector codebook, in case the number of divisions is threeor more, it is possible to expand similarly, so that achieving the casewherein the number of divisions is 2 will be described here

The codebook 4A includes a low-order vector codebook 41 _(L) storing Npieces of low-order code vectors x_(L1), . . . , x_(LN), and ahigh-order vector codebook 41 _(H) storing N′ pieces of high-order codevectors x_(H1), . . . , x_(HN′). Supposing the output code vector isx(n), in the low-order and high-order codebooks 41 _(L) and 41 _(H), 1to k- orders are defined as the low order and k+1to p-orders are definedas the high order among p-order, so that the codebooks are respectivelyformed of the vectors in the respective numbers of the dimensions.Namely, i-th vector of the low-order codebook 41 _(L) is expressed by:x_(Li)=(x_(Li1,)x_(Li2,) . . . , x_(Lik))  (9)and i′-th vector of the high-order vector codebook 41 _(H) is expressedby:x _(Hi′)=(x _(Hi′k+1,) x _(Hi′k+2,) . . . , x _(Hi′p))  (10)The inputted index Ix(n) is divided into Ix(n)_(L) and Ix(n)_(H), andcorresponding to these Ix(n)_(L) and Ix(n)_(H), the low-order andhigh-order split vectors x_(Li) and x_(Hi′) are respectively selectedfrom the respective codebooks 41 _(L) and 41 _(H), and these splitvectors x_(Li) and x_(Hi′) are integrated at an integrating part 47, tothereby generate the output code vector x(n). In other words, supposingthat the code vector outputted from the integrating part 47 is x(n),x(n)=(x _(Li1,) x _(Li2,) . . . , x _(Lik) |x _(Hi′k+1,) x _(Hi′k+2,) .. . , x _(Hi′p))  (11)is expressed.

In this embodiment, a low-order vector C_(0L) of the vector C₀ is storedas one of the vectors of the low-order codebook 41 _(L), and ahigh-order vector C_(0H) of the vector C₀ is stored as one of thevectors of the high-order codebook 41 _(H). As described above, there isachieved a structure which can output the following as the code vectorin case of corresponding to the silent interval or the stationary noiseinterval:C₀=(C_(0L)|C_(0H))  (12)Furthermore, depending on the case, the vector may be outputted as acombination of C_(0L) and the other high-order vector, or a combinationof the other low-order vector and C_(0H). If the split vector codebooks41 _(L) and 41 _(H) are provided as shown in FIG. 6, this is equivalentto providing the code vectors in the number of combinations between thetwo split vectors, there is an advantage that a size of each splitvector codebook can be reduced.

Fifth Embodiment

FIG. 7 shows a still another example of the configuration of the vectorcodebook 14A of the acoustic parameter coding device of FIG. 1 or thevector codebook 24A of the acoustic parameter decoding device of FIG. 2,wherein the codebook 4A is formed as a multi-stage and split vectorcodebook 4A. The codebook 4A is structured such that in the codebook 4Aof FIG. 4, the second-stage codebook 42 is formed of a half-split vectorcodebook as same as one in FIG. 6.

The first-stage codebook 41 N pieces of code vectors x₁₁, . . . ,x_(1N), a second-stage low-order codebook 42 _(L) stores N′ pieces oflow-order code vectors x_(2L1), . . . , x_(2LN′), and a second-stagehigh-order codebook 42 _(H) stores N″ pieces of high-order code vectorsx_(2H1), . . . , x_(2HN″).

In a code analysis part 43 ₁, the inputted index Ix(n) is analyzed intoan index Ix(n)₁ specifying the first-stage code vector, and an indexIx(n)₂ specifying the second-stage code vector. Then, i-th code vectorx_(1i) corresponding to the first-stage index Ix(n)_(i) is read out fromthe first-stage codebook 41. Also, the second-stage index Ix(n)₂ isanalyzed into Ix(n)_(2L) and Ix(n)_(2H), and by Ix(n)_(2L) andIx(n)_(2H), the respective i′-th and i″-th split vectors x_(2Li′) andx_(2Hi″) of the second-stage low-order split vector codebook 42 _(L) andthe second-stage high-order split vector codebook 42 _(H) are selected,and these selected split vectors are integrated at the integrating part47, to thereby generate the second-stage code vector x_(2i′i″). At theadding part 44, the first-stage code vector x_(1i) and the second-stageintegrated vector x_(2i′i″) are added together, to be outputted as thecode vector x(n).

In this embodiment, as in the embodiments of FIG. 4 and FIG. 5, thevector C₀ is stored as one of the vectors of the first-stage codebook41, and split zero vectors Z_(L) and Z_(H) are stored respectively asone of the vectors of the low-order split vector codebook 42 _(L) of thesecond-stage split codebook 42 and one of the vectors of the high-ordersplit vector codebook 42 _(H) of the second-stage split codebook 42. Asstructured as above, there is achieved a structure of outputting thecode vector in case of corresponding to the silent interval or thestationary noise interval. The number of the stages of the codebooks maybe three or more. Also, the split vector codebook can be used for any ofthe stages, and the number of the split codebooks per one stage is notlimited to two. Furthermore, if the search is conducted regarding thecode vectors of all of the combination between the first-stage codebook41 and the second-stage codebooks 42 _(L) and 42 _(H), the vector C₀ andthe split zero vectors Z_(L) and Z_(H) may be stored any of thecodebooks of the different stages from each other. Alternatively, as inthe second and third embodiments, storing the split zero vectors may beomitted.

In case they are not stored, the selection and addition from thecodebooks 42 _(L) and 42 _(H) are not carried out at the time ofselecting the vector C₀.

Sixth Embodiment

FIG. 8 is a multi-stage and split vector codebook 4A with scalingcoefficients, to which the present invention is applied, wherein thelow-order codebook 42 _(L) and the high-order codebook 42 _(H) of thesplit vector codebook 42 in the vector codebook 4A of the embodiment ofFIG. 7 is provided with scaling coefficient codebooks 45 _(L) and 45_(H) similar to the scaling coefficient codebook 45 in the embodiment ofFIG. 5. As coefficients by which the low-order and the high-order splitvectors are multiplied respectively, N pieces of coefficients in thevalue of about 0.5 to 2, for example, are stored in the low-orderscaling coefficient codebook 45 _(L) and the high-order scalingcoefficient codebook 45 _(H).

At an analysis part 43 ₁, the inputted index Ix(n) is analyzed into theindex Ix(n)₁ specifying the first-stage code vector and the index Ix(n)₂specifying the second-stage code vector. Firstly, the code vector x_(1i)corresponding to index Ix(n)₁ is obtained from the first-stage codebook41. Also, in correspondence with the index Ix(n)₁, a low-order scalingcoefficient S_(Li) and a high-order scaling coefficient S_(Hi) arerespectively read out from the low-order scaling coefficient codebook 45_(L) and the high-order scaling coefficient codebook 45 _(H). Then, theindex Ix(n)₂ is analyzed into an index Ix(n)_(2L) and an indexIx(n)_(2H) at an analysis part 43 ₂, and respective split vectorsx_(2Li′) and x_(2Hi″) of the second-stage low-order split vectorcodebook 42 _(L) and the second-stage high-order split vector codebook42 _(H) are selected by these indexes Ix(n)_(2L) and Ix(n)_(2H). Theseselected split vectors are multiplied by the low-order and high-orderscaling coefficients S_(Li) and S_(Hi) at multipliers 46 _(L) and 46_(H), and the obtained multiplied vectors are integrated at anintegrating part 47, to thereby generate a second-stage code vectorx_(2i′i″). The first-stage code vector x_(1i) and the second-stageintegrated vector x_(2i′i″), are added together at the adder 44, and theadded result is outputted as the code vector x(n).

In the multi-stage and split vector codebook 4A with scalingcoefficients of the embodiment, the vector C₀ is stored as one of thecode vectors in the first-stage codebook 41, and the split zero vectorsZ_(L) and Z_(H) are respectively stored as the split vectors in thelow-order split vector codebook 42 _(L) and the high-order split vectorcodebook 42 _(H) of the second-stage split vector codebook as well.Accordingly, there is achieved a configuration of outputting the codevector in the case of corresponding to the silent interval or thestationary noise interval. The number of the stages of the codebook maybe three or more. In this case, two or more stages subsequent to thesecond-stage can be respectively formed of the split vector codebooks.Also, in either case, it is not limited to the number of the splitvector codebooks per stage.

Seventh Embodiment

FIG. 9 illustrates a still further example of a configuration of thevector codebook 14A of the acoustic parameter coding device of FIG. 1 ofthe vector codebook 24A of the acoustic parameter decoding device ofFIG. 2, and the first-stage codebook 41 of the embodiment of FIG. 7 isalso formed of split vector codebooks as in the embodiment of FIG. 6. Inthis embodiment, N pieces of high-order split vectors x_(1L1), . . . ,x_(1LN) are stored in the first-stage low-order codebook 41 _(L), and N′pieces of high-order split vectors x_(1H1), . . . , x_(1HN′) are storedin the first-stage high-order codebook 41 _(H). N″ pieces of low-ordersplit vectors x_(2L1), . . . , x_(2LN″) are stored in the second-stagelow-order codebook 42 _(L), and N′″ pieces of high-order split vectorsx_(2H1), . . . , x_(2HN′″) are stored in the second-stage high-ordercodebook 42 _(H).

At the code analysis part 43, the inputted index Ix(n) is analyzed intothe index Ix(n)₁ specifying the first-stage code vector and the indexIx(n)₂ specifying the second-stage code vector. Respective i-th and i′thsplit vectors x_(1Li) and x_(1Hi′) of the first-stage split vectorcodebook 41 _(L) and the first-stage high-order codebook 41 _(H) areselected as vectors corresponding to the first-stage index Ix(n)₁, andthe selected vectors are integrated at an integrating part 47 ₁, tothereby generate a first-stage integrated vector x_(1ii′).

Also, similarly to the first stage, regarding the second-stage indexIx(n)₂, respective i″-th and i′″th split vectors x_(2Li″) and x_(2Hi′″)of the second-stage split vector codebook 42 _(L) and the second-stagehigh-order codebook 42 _(H) are selected, and the selected vectors areintegrated at an integrating part 47 ₂, to thereby generate asecond-stage integrated vector x_(2i″i′″). At the adding part 44, thefirst-stage integrated vector x_(1ii′) and the second-stage integratedvector x_(2i″i′″) are added together, and the added result is outputtedas the code vector x(n).

In this embodiment, similarly to the configuration of the split vectorcodebook of FIG. 6, at the first stage, the low-order split vectorC_(0L) of the vector C₀ is stored as one of the vectors of the firststage low-order codebook 41 _(L), and the high-order split vector C_(0H)of the vector C₀ is stored as one of the vectors of the first-stagehigh-order codebook 41 _(H). In addition, the split zero vectors Z_(L)and Z_(H) are respectively stored as the respective ones of vectors ofthe low-order split vector codebook 42 _(L) of the second-stage splitvector codebook 42 and the high-order split vector codebook 42 _(H) ofthe second stage. According to this configuration, there is achieved aconfiguration which enable to output the code vector in the case ofcorresponding to the silent interval or the stationary noise interval.Also in this case, the number of the multi stages is not limited to two,and the number of the split vector codebooks per stage is not limited totwo.

Eighth Embodiment

FIGS. 10A and 10B are block diagrams illustrating configurations ofspeech signal transmission device and receiving device to which thepresent invention is applied.

A speech signal 101 is converted into an electric signal by an inputdevice 102, and outputted to an A/D converter 103. The A/D converterconverts the (analog) signal outputted from the input device 102 into adigital signal, and output it to a speech coding device 104. The speechcoding device 104 encodes the digital speech signal outputted from theA/D converter 103 by using a speech coding method, described later, andoutputs the encoded information to an RF modulator 105. The RF modulator105 converts the speech encoded information outputted from the speechcoding device 104 into a signal to be sent out by being placed on apropagation medium, such as a radio wave, and outputs the signal to atransmitting antenna 106. The transmitting antenna 106 transmits theoutput signal outputted from the RF modulator 105 as the radio wave (RFsignal) 107. The foregoing is the configuration and operations of thespeech signal transmission device.

The transmitted radio wave (RF signal) 108 is received by a receivingantenna 109, and outputted to an RF demodulator 110.

Incidentally, the radio wave (RF signal) 108 in the figure constitutesthe radio wave (RF signal) 107 as seen from the receiving side, and ifthere is no damping of signal or superposition of the noise in thepropagation channel, the radio wave 108 constitutes the exactly same oneas the radio wave (RF signal) 107. The RF demodulator 110 demodulatesthe speech encoded information from the RF signal outputted from thereceiving antenna 109, and outputs the same to a speech decoding device111. The speech decoding device 111 decodes the speech signal from thespeech encoded information by using the speech decoding method,described later, and outputs the same to a D/A converter 112. The D/Aconverter 112 converts the digital speech signal outputted from thespeech decoding device 111 into an analog electric signal and output itto an output device 113. The output device 113 converts the electricsignal into vibration of air, and outputs as a sound wave 114 so thatthe human being can hear by ears. The foregoing is the configuration andoperations of the speech signal receiving device.

By having at least one of the aforementioned speech signal transmissiondevice and receiving device, a base station and mobile terminal devicein the mobile communication system can be structured.

The aforementioned speech signal transmission device is characterized inthe speech coding device 104. FIG. 11 is a block diagram illustrating aconfiguration of the speech coding device 104.

An input speech signal constitutes the signal outputted from the A/Dconverter 103 in FIG. 10A, and is inputted into a preprocessing part200. In the preprocessing part 200, there are conducted a waveformshaping process and a preemphasis process, which might be connected toimprovement of performances in high-pass filter processing for removingDC components or subsequent coding process, and a processed signal Xinis outputted to an LPC analysis part 201 and an adder 204, and then to aparameter determining part 212. The LPC analysis conducts the linearprediction analysis of Xin, and the analyzed result (linear predictivecoefficient) is outputted to an LPC quantization part 202. The LPCquantization part 202 is formed of an LSP parameter calculating part 13,a parameter coding part 10, a decoding part 18, and a parameterconverting part 19. The parameter coding part 10 has the sameconfiguration as the parameter coding part 10 in FIG. 1 to which thevector codebook of the invention according to one of the embodiments ofFIGS. 3 to 9 is applied. Also, the decoding part 18 has the sameconfiguration as the decoding device in FIG. 2, to which one of thecodebooks of FIGS. 3 to 9.

The linear predictive coefficient (LPC) outputted from the LPC analysispart 201 is converted into the LSP parameter at the LSP parametercalculating part 13, and the obtained LSP parameter is encoded at theparameter coding part 10 as explained with reference to FIG. 1. Thevectors Ix(n) and Iw(n) obtained by encoding, that is, the code Lshowing the quantized LPC is outputted to a multiplexing part 213. Atthe same time, these codes Ix(n) and Iw(n) are decoded at the decodingpart 18 to obtain the quantized LSP parameter, and the quantized LSPparameter is converted again into the LPC parameter at the parameterconverting part 19, so that the obtained quantized LPC parameter isgiven to a synthesis filter 203. By having the quantized LPC as a filtercoefficient, the synthesis filter 203 synthesizes the acoustic signal bya filter process with respect to a drive sound source signal outputtedfrom an adder 210, and outputs the synthesized signal to the adder 204.

The adder 204 calculates an error signal ε between the aforementionedXin and the aforementioned synthesized signal, and outputs the same to aperceptual weighting part 211. The perceptual weighting part 211conducts the perceptual weighting with respect to the error signal εoutputted from the adder 204, and calculates a distortion of thesynthesized signal with respect to Xin in a perceptual weighting area,to thereby output it to the parameter determining part 212. Theparameter determining part 212 determines the signals that should begenerated by an adaptive codebook 205, a fixed codebook 207 and aquantized gain generating part 206 such that the coding distortionoutputted from the perceptual weighting part 211 becomes a minimum.Incidentally, not only minimizing the coding distortion outputted fromthe perceptual weighting part 211, but also using a method of minimizinganother coding distortion by using the aforementioned Xin, to therebydetermine the signal generated from the aforementioned three means, thecoding performance can be further improved.

The adaptive codebook 205 conducted buffering of the sound source signalof the preceding frame n−1, that was outputted from the adder 210 in thepast when the distortion was minimized, and cuts out the sound vectorfrom a position specified by an adaptive vector code A thereof outputtedfrom the parameter determining part 212, to thereby repeatedlyconcatenate the same until it becomes the length of one frame, resultingin generating the adaptive vector including a desired periodic componentand outputting the same to a multiplier 208. In the fixed codebook 207,a plurality of fixed vectors each having the length of one frame arestored in correspondence with the fixed vector codes, and outputs afixed vector, which has a form specified by a fixed vector code Foutputted from the parameter determining part 212, to a multiplier 209.

The quantized gain generating part 206 respectively provides themultipliers 208 and 209 with an adaptive vector, that is specified by again code G outputted from the parameter determining part 212, aquantized adaptive vector gain g_(A) and a quantized adaptive vectorgain g_(F) with respect to the fixed vector. In the multiplier 208, thequantized adaptive vector gain g_(A) outputted from the quantized gaingenerating part 206 is multiplied by the adaptive vector outputted fromthe adaptive codebook 205, and the multiplied result is outputted to theadder 210. In the multiplier 209, the quantized fixed vector gain g_(F)outputted from the quantized gain generating part 206 is multiplied bythe fixed vector outputted from the fixed codebook 207, and themultiplied result is outputted to the adder 210.

In the adder 210, the adaptive vector and the fixed vector aftermultiplying with the gains are added together, and the added result isoutputted to the synthesis filter 203 and the adaptive codebook 205.Finally, in the multiplexing part 213, the code L indicating thequantized LPC is inputted from the LPC quantization part 202; theadaptive vector code A indicating the adaptive vector, the fixed vectorcode F indicating the fixed vector, and the gain code G indicating thequantized gains are inputted from the parameter determining part 212;and these codes are multiplexed to be outputted as the encodedinformation to the transmission path.

FIG. 12 is a block diagram illustrating a configuration of the speechdecoding device 111 in FIG. 10B.

In the figure, regarding the encoded information outputted from the RFdemodulator 110, the multiplexed encoded information is separated by ademultiplexing part 1301 into individual codes L, A, F and G. Theseparated LPC code L is given to an LPC decoding part 1302; theseparated adaptive vector code A is given to an adaptive codebook 1305;the separated gain code G is given to a quantized gain generating part1306; and the separated fixed vector code F is given to a fixed codebook1307. The LPC decoding part 1302 is formed of a decoding part 1302Aconfigured as same as that of FIG. 2, and a parameter converting part1302B. The code L=(Ix(n), Iw(n)) provided from the demultiplexing part1301 is decoded in the LSP parameter area by the decoding part 1302A asshown in FIG. 2, and converted into an LPC, to thereby be outputted to asynthesis filter 1303.

The adaptive codebook 1305 takes out an adaptive vector from a positionspecified by the adaptive vector code A outputted from thedemultiplexing part 1301, and outputs the same to a multiplier 1308. Thefixed codebook 1307 generates a fixed vector specified by the fixedvector code F outputted from the demultiplexing part 1301, and outputsthe same to a multiplier 1309. The quantized gain generating part 1306decodes the adaptive vector gain g_(A) and the fixed vector gain g_(F),which are specified by the gain code G outputted from the demultiplexingpart 1301, and respectively output them to the multipliers 1308 and1309. In the multiplier 1308, the adaptive code vector is multiplied bythe aforementioned adaptive code vector gain g_(A), and the multipliedresult is outputted to an adder 1310. In the multiplier 1309, the fixedcode vector is multiplied by the aforementioned fixed code vector gaing_(F), and the multiplied result is outputted to the adder 1310. In theadder 1310, the adaptive vector and the fixed vector, which areoutputted from the multipliers 1308 and 1309 after multiplying with thegains, are added together, and the added result is outputted to thesynthesis filter 1303. In the synthesis filter 1303, by having thevector outputted from the adder 1310 as a drive sound source signal, thefilter synthesis is conducted by using a filter coefficient decoded bythe LPC decoding part 1302, and the synthesized signal is outputted to apostprocessing part 1304. The postprocessing part 1304 conducts aprocess for improving a subjective quality of the speech, such asformant emphasis or pitch emphasis, or conducts a process for improvinga subjective quality of the stationary noise, and thereafter outputs asa final decoded speech signal.

Although the LSP parameter is used as the parameter equivalent to thelinear predictive coefficient indicating the spectrum envelope in theaforementioned description, other parameters, such as α parameter,PARCOR coefficient and the like, can be used. In the case of using theseparameters, since the spectrum envelope also becomes flat in the silentinterval or the stationary noise interval, the computation of theparameter at these intervals can be conducted easily, and in the case ofp-order α parameter, for example, it will suffice that 0-order is 1.0and 1- to p-order is 0.0. Even in the case of using other acousticparameters, a vector of the acoustic parameter determined to indicatesubstantially flat spectrum envelope will suffice. Incidentally, the LSPparameter is practical since the quantization efficiency thereof isgood.

In the foregoing description, in the case that the vector codebook isstructured as the multi-stage configuration, the vector C₀ may beexpressed by two synthesis vectors, for example, C₀=C₀₁+C₀₂, and C₀₁ andC₀₂ may be stored in the codebooks of the different stages from eachother.

Furthermore, the present invention is applied not only to coding anddecoding of the speech signal, but also to coding and decoding ofgeneral acoustic signal, such as a music signal.

Also, the device of the invention can carry out coding and decoding ofthe acoustic signal by running the program by the computer. FIG. 13illustrates an embodiment in which a computer conducts the acousticparameter coding device and decoding device of FIGS. 1 and 2 using oneof the codebooks of FIGS. 3 to 9, and the acoustic signal coding deviceand the decoding device of FIGS. 11 and 12 to which the coding methodand decoding method thereof are applied.

The computer which carries out the present invention is formed of amodem 410 connected to a communication network; an input and outputinterface 420 for inputting and outputting the acoustic signal; a buffermemory 430 for temporarily storing a digital acoustic signal or theacoustic signal; a random access memory (RAM) 440 for carrying out thecoding and decoding processes therein; a central processing unit (CPU)450 for controlling the input and output of the data and programexecution; a hard disk 460 in which the coding and decoding program isstored; and a drive 470 for driving a record medium 470M. Thesecomponents are connected by a common bus 480.

As the record medium 470M, there can be used any kinds of record media,such as a compact disc CD, a digital video disc DVD, a magneto-opticaldisk MO, a memory card, and the like. In the hard disk 460, there isstored the program in which the coding method and the decoding methodconducted in the acoustic signal coding device and decoding device ofFIGS. 11 and 12 are expressed by procedures by the computer. Thisprogram includes a program, as a subroutine, for carrying out theacoustic parameter coding and decoding of FIGS. 1 and 2.

In the case of encoding the input acoustic signal, CPU 450 loads anacoustic signal coding program from the hard disk 460 into RAM 440; theacoustic signal imported into the buffer memory 430 is encoded byconducting the process per frame in RAM 440 in accordance with thecoding program; and obtained code is send out as the encoded acousticsignal data via the modem 410, for example, to the communicationnetwork. Alternatively, the data is temporarily saved in the hard disk460. Or, the data is written on the record medium 470M by the recordmedium drive 470.

In the case of decoding the input encoded acoustic signal, CPU 450 loadsa decoding program from the hard disk 460 into RAM 440. Then, theacoustic code data is downloaded to the buffer memory 430 via the modem410 from the communication network, or loaded to the buffer memory 430from the record medium 470M by the drive 470. CPU 450 processes theacoustic code data per frame in RAM 440 in accordance with the decodingprogram, and obtained acoustic signal data is outputted from the inputand output interface 420.

EFFECT OF THE INVENTION

FIG. 14 shows quantization performances of the acoustic parameter codingdevices in the case of embedding the zero vector C₀ at the silentinterval and the zero vector z in the codebook according to the presentinvention and in the case of not embedding the vector C₀ in the codebookas in the conventional one. In FIG. 14, the axis of ordinate is cepstrumdistortion, which corresponds to the log spectrum distortion, shown indecibel (dB). The smaller cepstrum distortion is, the better thequantization performance is. Also, as the speech intervals for computingthe distortion, the mean distortions are found in the average of all ofthe intervals (Total), in the interval other than the silent intervaland the stationary interval of the speech (Mode 0), and in thestationary interval of the speech (Mode 1). One in which the silentinterval exists is Mode 0, and regarding the distortions therein, thatof the proposed codebook is 0.11 dB lower, and it is understood thatthere is the effect by inserting the silent and zero vectors. Also,regarding the cepstrum distortion in Total, the distortion in case ofusing the proposed codebook is lower, and since there is nodeterioration in the speech stationary interval, the effectiveness ofthe codebook according to the present invention is obvious.

As described above, according to the present invention, in codingwherein the parameter equivalent to the linear predictive coefficient isquantized by the weighted sum of the code vector of the current frameand the code vector outputted in the past, or the vector in which theabove sum and mean vector found in advance are added together, as thevector stored in the vector codebook, the parameter vector correspondingto the silent interval or the stationary noise interval, or a vector inwhich the aforementioned mean vector is subtracted from the parametervector is selected as the code vector, and the code thereof can beoutputted. Therefore, there can be provided the coding and decodingmethods and the devices thereof in which the quality deterioration inthese intervals is scarce.

1. An acoustic parameter coding method, comprising: (a) a step ofcalculating an acoustic parameter equivalent to a linear predictivecoefficient showing a spectrum envelope characteristic of an acousticsignal for every frame of a predetermined length of time; (b) a step ofmultiplying a code vector outputted in at least one frame in the closestpast selected from a vector codebook for storing a plurality of codevectors in correspondence with an index representing said code vectorsand a code vector selected in a current frame respectively with a set ofweighting coefficients selected from a coefficient codebook for storingone or more sets of weighting coefficients in correspondence with anindex representing the weighting coefficients, wherein multipliedresults are added to generate a weighted vector and a vector including acomponent of said weighted vector is found as a candidate of a quantizedacoustic parameter with respect to said acoustic parameter of thecurrent frame; and (c) a step of determining the code vector of thevector codebook and the set of the weighting coefficients of thecoefficient codebook by using a standard such that a distortion of saidcandidate of the quantized acoustic parameter with respect to thecalculated acoustic parameter becomes a minimum, wherein an indexshowing the determined code vector and the determined set of theweighting coefficients are determined and outputted as a quantized codeof the acoustic parameter.
 2. In the coding method according to claim 1,wherein said vector codebook includes a vector having a component of anacoustic parameter vector showing a substantially flat spectrum envelopeas one of the stored code vectors.
 3. In the coding method according toclaim 2, said vector codebook is formed of codebooks in plural stageseach storing a plurality of vectors in correspondence with an indexrepresenting the vectors, a codebook at one stage of said codebooks inthe plural stages stores said vector including the component of theacoustic parameter vector showing the substantially flat spectrumenvelope as one of the stored vectors, another codebook at another stageof the codebooks in the plurality of stages stores a zero vector as oneof the stored vectors, and said step (b) includes a step of respectivelyselecting vectors from the codebooks in the plural stages and adding theselected vectors together to thereby output an added result as saidvector selected in the current frame.
 4. In the coding method accordingto claim 2, said vector codebook is formed of codebooks in plural stageseach storing a plurality of vectors in correspondence with an indexrepresenting the vectors, a codebook at one stage of the codebooks inthe plural stages stores said vector including the component of theacoustic parameter vector showing the substantially flat spectrum as oneof the stored vectors, said step (b) further includes a step ofrespectively selecting vectors from the codebooks in the plural stageswhen a code vector other than said vector including the parameter vectoris selected from the codebook at said one stage of the codebooks in theplural stages and adding the selected vectors together to thereby outputan added result as the code vector selected in the current frame,wherein in case said vector including the component of the acousticparameter vector showing the substantially flat spectrum envelope isselected from the codebook at said one stage, said vector including thecomponent of the acoustic parameter vector showing the substantiallyflat spectrum envelope is outputted as said vector selected in thecurrent frame.
 5. In the coding method according to claim 3 or 4, acodebook of at least one of the stages of the codebooks in the pluralstages includes a plurality of split vector codebooks for divisionallystoring a plurality of split vectors in which dimensions of code vectorsare divided in plural, and an integrating part for integrating the splitvectors outputted from the plurality of split vector codebooks tothereby output the same as an output vector of the codebook of thecorresponding stage.
 6. In the coding method according to claim 3 or 4,said vector including the component of the acoustic parameter vectorshowing the substantially flat spectrum envelope is a vector generatedby subtracting a mean vector of parameters equivalent to the linearpredictive coefficient in an entirety of the acoustic signal and foundin advance from said parameter vector equivalent to the linearpredictive coefficient.
 7. In the coding method according to any one ofclaims 3 and 4, said steps (b) and (c) collectively include firstly astep of searching a predetermined number of code vectors such that adistortion due to the code vector selected from the codebook of said onestage is a minimum, and subsequently a step of finding said distortionsfor all of combinations between said predetermined number of the codevectors and code vectors each being selected one by one from codebooksof the remaining stages, to thereby determine a code vector of acombination in which the distortion becomes the minimum.
 8. In thecoding method according to claim 2, said vector codebook includescodebooks in plural stages each storing a plurality of code vectors, andscaling coefficient codebooks respectively provided with respect to therespective codebooks of a second stage and stages after the secondstage, each of said scaling coefficient codebooks storing scalingcoefficients determined in advance in accordance with respective codevectors of a codebook at a first stage, a codebook at one stage of saidcodebooks in the plural stages stores said vector including thecomponent of the acoustic parameter vector showing the substantiallyflat spectrum as one of the stored vectors, each of other codebooks ofthe remaining stages storing a zero vector, wherein said step (b)comprises: a step of reading out scaling coefficients from the scalingcodebooks on and after the second stage in correspondence with a codevector selected at the first stage, and multiplying the code vectorselected at the first stage with each of the selected code vectors, tothereby output multiplied results as vectors of the respective stages;and a step of adding the outputted vectors of the respective stages tothe vector at the first stage, to thereby output an added result as acode vector from the vector codebook.
 9. In the coding method accordingto claim 8, a codebook at least one stage on and after the second stageamong said codebooks in the plural stages is formed of a plurality ofsplit vector codebooks divisionally storing a plurality of split vectorsin which dimensions of the code vectors are divided in plural, saidscaling coefficient codebook corresponding to the codebook of said atleast one stage includes a plurality of scaling coefficient codebooksfor the split vectors provided with respect to the plurality of splitvector codebooks, and scaling coefficients for split vectors in whicheach of code vectors of the respective scaling coefficient codebooks forthe split vectors is found in advance with respect to each of the codevectors of the codebook at the first stage, wherein said step (b)comprises: a step of reading out a scaling coefficient for a splitvector in correspondence with the index of the vector selected at thecodebook of the first stage and respectively multiplying the same withsplit vectors respectively selected from the plurality of split vectorcodebooks of said at least one stage; and a step of integrating splitvecotrs obtained by said multiplying to thereby output integratedresults as output vectors of the codebooks at the respective stages. 10.In the coding method according to claim 2, said vector codebook isformed of a plurality of split vector codebooks in which dimensions ofthe code vectors are divided in plural, and an integrated part forintegrating split vectors outputted from the split vector codebooks tothereby output a result as one code vector, said vector including thecomponent of the acoustic parameter vector showing the substantiallyflat spectrum envelope is divisionally stored in each of the pluralityof split vector codebooks as a split vector.
 11. In the coding methodaccording to claim 2, said vector including the component of theacoustic parameter vector showing the substantially flat spectrumenvelope is a vector generated by subtracting a mean vector from saidacoustic parameter vector showing the linear predictive coefficient, andsaid step (b) includes a step of adding said weighted vector to a meanvector of parameters equivalent to the linear predictive coefficient inan entirety of the acoustic signal found in advance, to thereby generatethe vector including the component of the weighted vector.
 12. In thecoding method according to claim 2, the parameter equivalent to thelinear predictive coefficient constitutes an LSP parameter.
 13. Anacoustic signal coding method for encoding an input acoustic signal,comprising: (A) a step of encoding a spectrum characteristic of an inputacoustic signal by using the acoustic parameter coding method accordingto claim 2; (B) a step of using as an excitation signal a sound sourcevector generated based on an adaptive code vector from an to adaptivecodebook for holding adaptive code vectors showing periodic componentsof an input acoustic signal therein and a fixed vector from a fixedcodebook for storing a plurality of fixed vectors therein, and carryingout a synthesis filter process by a filter coefficient based on saidquantized acoustic parameter to thereby generate a synthesized acousticsignal; and (C) a step of determining an adaptive code vector and afixed vector selected from the fixed codebook and the adaptive codebooksuch that a distortion of the synthesized acoustic signal with respectto the input acoustic signal becomes small, and outputting an adaptivecode and a fixed code respectively corresponding to the determinedadaptive code vector and the fixed vector.
 14. A program for conductingthe acoustic parameter coding method according to any one of claims 3,4, 8, 9 and 2 by a computer.
 15. The coding method of claim 1 or 2,wherein said vector codebook includes codebooks in plural stages eachstoring a plurality of code vectors, and scaling coefficient codebooksrespectively provided with respect to the respective codebooks of asecond stage and stages after the second stage, each of said scalingcoefficient codebooks storing scaling coefficients determined in advancein accordance with respective code vectors of a codebook at a firststage, and a codebook of at least one stage on or after the second stageamong said codebooks in the plural stages is formed of a plurality ofsplit vector codebooks divisionally storing a plurality of split vectorsin which dimensions of the code vectors are divided in plural, saidscaling coefficient codebook corresponding to the codebook of said atleast one stage includes a plurality of scaling coefficient codebooksfor the split vectors provided with respect to the plurality of splitvector codebooks, and each storing scaling coefficients for splitvectors predetermined in correspondence with the codebook at the firststage, wherein said step (b) comprises: a step of reading out scalingcoefficients from the scaling codebooks of the second and subsequentstages in correspondence with a code vector selected at the first stage,and multiplying the scaling coefficients with the selected code vectors,respectively, to thereby output multiplied results as vectors of thesecond and subsequent stages; and a step of adding the outputted vectorsof the second and subsequent stages to the vector at the first stage, tothereby output an added result as a code vector from the vectorcodebook, wherein said step of outputting the vector from said codebookof said at least one stage comprises: a step of reading out scalingcoefficients from said plurality of scaling coefficient codebooks for asplit vector in correspondence with the index of the vector selected atthe codebook of the first stage and respectively multiplying the scalingcoefficients with split vectors respectively selected from the pluralityof split vector codebooks of said at least one stage to producemultiplied split vectors; and a step of integrating said multipliedsplit vectors to thereby output an integrated result as an output vectorof the codebook at said at least one stage.
 16. An acoustic parameterdecoding method, comprising: (a) a step of outputting a code vectorcorresponding to an index expressed by a code inputted for every frameand a set of weighting coefficients from a vector codebook and acoefficient codebook, said vector codebook storing a plurality of codevectors of an acoustic parameter equivalent to a linear predictivecoefficient showing a spectrum envelope characteristic of an acousticsignal in correspondence with an index representing the code vectors,said coefficient codebook storing one or more sets of weightingcoefficients in correspondence with an index representing said sets; and(b) a step of multiplying said code vector outputted from said vectorcodebook in at least one frame of the closest past and a code vectoroutputted from the vector codebook in a current frame respectively withsaid outputted set of the weighting coefficients, and adding multipliedresults together to thereby generate a weighted vector, wherein a vectorincluding a component of said weighted vector is outputted as a decodedquantized vector of the current frame.
 17. In the decoding methodaccording to claim 16, wherein said vector codebook includes a vectorhaving a component of an acoustic parameter vector showing asubstantially flat spectrum envelope as one of the code vectors storedtherein.
 18. In the decoding method according to claim 17, said vectorcodebook is formed of codebooks in plural stages each storing aplurality of vectors in correspondence with an index representing thevectors, a codebook at one stage of the codebooks in plural stagesstores said vector including the component of the acoustic parametervector showing the substantially flat spectrum envelope, codebooks ofthe other stages storing zero vectors as one of the vectors, and saidstep (b) includes a step of respectively outputting vectors specified bythe index expressed by the inputted code from the codebooks in theplural stages, in which the outputted vectors are added and an addedresult is outputted as a code vector in the current frame.
 19. In thedecoding method according to claim 17, said vector codebook is formed ofcodebooks in plural stages each storing a plurality of vectors incorrespondence with an index representing the vectors, a codebook at onestage of the codebooks in plural stages stores said vector including thecomponent of the acoustic parameter vector showing the substantiallyflat spectrum envelope as one of the vectors, said step (b) includes astep of respectively selecting vectors from the codebooks in the pluralstages when a code vector other than said vector including the componentof the acoustic parameter vector showing the substantially flat spectrumenvelope is selected from the codebook at said one stage of thecodebooks in the plural stages and adding the selected vectors togetherto thereby output an added result as the code vector selected in thecurrent frame, wherein in case said vector including the component ofthe acoustic parameter vector showing the substantially flat spectrumenvelope is selected from the codebook at said one stage, said vectorincluding the component of the acoustic parameter vector showing thesubstantially flat spectrum envelope is outputted as said vector of thecurrent frame.
 20. In the decoding method according to claim 18 or 19, acodebook, of at least one of the stages of the codebooks in the pluralstages includes a plurality of split vector codebooks for divisionallystoring a plurality of split vectors in which dimensions of code vectorsare divided in plural, and an integrating part for integrating the splitvectors outputted from the plurality of split vector codebooks tothereby output the same as an output vector of the codebook of thecorresponding stage.
 21. In the decoding method according to claim 18 or19, said vector including the component of the parameter vectorequivalent to the linear predictive coefficient is a vector generated bysubtracting a mean vector of parameters equivalent to the linearpredictive coefficient in an entirety of the acoustic signal and foundin advance from said parameter vector equivalent to the linearpredictive coefficient.
 22. In the decoding method according to claim17, said vector codebook includes codebooks in plural stages eachstoring a plurality of code vectors, and scaling coefficient codebooksrespectively provided with respect to the respective codebooks of asecond stage and stages after the second stage, each of said scalingcoefficient codebooks stores scaling coefficients determined in advancein correspondence with code vectors of a codebook at a first stage, acodebook at one stage of said codebooks in the plural stages storingsaid vector including the component of the acoustic parameter vectorshowing the substantially flat spectrum as one of the stored vectors,each of other codebooks of the remaining stages storing a zero vector,wherein said step (b) comprises: a step of reading out scalingcoefficients from the scaling codebooks on and after the second stage incorrespondence with a code vector selected at the first stage, andmultiplying the code vector selected at the first stage with each of theselected code vectors, to thereby output multiplied results as vectorsof the respective stages; and a step of adding the outputted vectors ofthe respective stages to the vector at the first stage, to therebyoutput an added result as a code vector from the vector codebook.
 23. Inthe decoding method according to claim 22, a codebook at at least onestage on and after the second stage among said codebooks in the pluralstages is formed of a plurality of split vector codebooks divisionallystoring a plurality of split vectors in which dimensions of the codevectors are divided in plural, said scaling coefficient codebookcorresponding to the codebook of said at least one stage includes aplurality of scaling coefficient codebooks for the split vectorsprovided with respect to the plurality of split vector codebooks, saidscaling coefficient codebook for split vectors stores a plurality ofscaling coefficients for split vectors in correspondence with therespective code vectors of the codebook of the first stage, wherein saidstep (b) comprises: a step of reading out a scaling coefficient for asplit vector in correspondence with the index of the vector selected atthe codebook of the first stage and respectively multiplying the samewith split vectors respectively selected from the plurality of splitvector codebooks of said at least one stage, and a step of integratingsplit vectors obtained by said multiplying to thereby output integratedresults as output vectors of the codebooks at the respective stages. 24.In the decoding method according to claim 17, said vector codebook isformed of a plurality of split vector codebooks in which dimensions ofthe code vectors are divided in plural, and an integrating part forintegrating split vectors outputted from the split vector codebooks tothereby output a result as one code vector, said vector including thecomponent of the acoustic parameter vector showing the substantiallyflat spectrum envelope is divided into split vectors to be divisionallystored in each of the plurality of split vector codebooks as a splitvector.
 25. In the decoding method according to claim 17, said vectorincluding the component of the acoustic parameter vector showing thesubstantially flat spectrum envelope is a vector generated in advance bysubtracting said mean vector from said acoustic parameter vector showingthe linear predictive coefficient, and said step (b) includes a step ofadding said weighted vector and a mean vector of parameters equivalentto the linear predictive coefficient in an entirety of the acousticsignal found in advance, to thereby generate the vector including thecomponent of the weighted vector.
 26. In the decoding method accordingto claim 17, the parameter equivalent to the linear predictivecoefficient constitutes an LSP parameter.
 27. An acoustic signaldecoding device for decoding an input code and outputting an acousticsignal, comprising: means for decoding an acoustic parameter equivalentto a linear predictive coefficient showing a spectrum envelopecharacteristic from an inputted code by using the acoustic parameterdecoding method according to claim 17; a fixed codebook for storing aplurality of fixed vectors therein; an adaptive codebook for holdingadaptive code vectors showing periodic components of a synthesizedacoustic signal therein; means for taking out a corresponding fixedvector from the fixed codebook and taking out a corresponding adaptivecode vector from the adaptive codebook by an inputted adaptive code andan inputted fixed code, the means synthesizing the vectors andgenerating an excitation vector; and filtering means for setting afilter coefficient based on the acoustic parameter and reproducing anacoustic signal by the excitation vector.
 28. An acoustic signaldecoding method for decoding input codes and outputting an acousticsignal, comprising: (A) a step of decoding an acoustic parameterequivalent to a linear predictive coefficient showing a spectrumenvelope characteristic from inputted codes by using the acousticparameter decoding method according to claim 17, (B) a step of takingout a corresponding adaptive code vector from an adaptive codebook forholding therein adaptive code vectors showing periodic components of aninput acoustic signal by an adaptive code and a fixed code among theinputted codes, taking out a corresponding fixed vector from a fixedcodebook for storing a plurality of fixed vectors therein, andsynthesizing the adaptive code vector and the fixed vector to therebygenerate an excitation vector; and (C) a step of carrying out asynthesis filter process of the excitation vector by using a filtercoefficient based on the acoustic parameter, and reproducing asynthesized acoustic signal.
 29. A program for conducting the acousticparameter decoding method according to any one of claims 18, 19, 22, 26and 17 by a computer.
 30. The decoding method of claim 16 or 17, whereinsaid vector codebook includes codebooks in plural stages each storing aplurality of code vectors, and scaling coefficient codebooksrespectively provided with respect to the respective codebooks of asecond stage and stages after the second stage, each of said scalingcoefficient codebooks stores scaling-coefficients determined in advancein correspondence with code vectors of a codebook at a first stage,wherein a codebook at at least one stage on or after the second stageamong said codebooks in the plural stages is formed of a plurality ofsplit vector codebooks divisionally storing a plurality of split vectorsin which dimensions of the code vectors are divided in plural, saidscaling coefficient codebook corresponding to the codebook of said atleast one stage includes a plurality of scaling coefficient codebooksfor the split vectors provided with respect to the plurality of splitvector codebooks, each of said sealing coefficient codebooks for splitvectors stores a plurality of scaling coefficients for split vectors incorrespondence with the respective code vectors of the codebook of thefirst stage, wherein said step (b) comprises: a step of reading outscaling coefficients from the scaling codebooks of the second andsubsequent stages in correspondence with a code vector selected at thefirst stage, and multiplying the scaling coefficients with the selectedcode vectors, respectively, to thereby output multiplied results asvectors of the second and subsequent stages; a step of adding theoutputted vectors of the respective stages to the vector at the firststage, to thereby output an added result as a code vector from thevector codebook; wherein said step of outputting the vector from saidcodebook of said at least one stage includes: a step of reading outsealing coefficients from said plurality of scaling coefficientcodebooks for a split vector in correspondence with the index of thevector selected at the codebook of the first stage and respectivelymultiplying the scaling coefficients with split vectors respectivelyselected from the plurality of split vector codebooks of said at leastone stage to produce multiplied split vectors, and a step of integratingsaid multiplied split vectors to thereby output an integrated result asan output vector of the codebook at said at least one stage.
 31. Anacoustic parameter coding device, comprising: parameter calculatingmeans for analyzing an input acoustic signal for every frame andcalculating an acoustic parameter equivalent to a linear predictivecoefficient showing a spectrum envelope characteristic of the acousticsignal; a vector codebook for storing a plurality of code vectors incorrespondence with an index representing the vectors; a coefficientcodebook for storing one or more sets of weighting coefficients incorrespondence with an index representing the coefficients; quantizedparameter generating means for multiplying a code vector with respect toa current frame outputted from the vector codebook and a code vectoroutputted in at least one frame of the closest past respectively withthe set of the weighting coefficients selected from the coefficientcodebook, said quantized parameter generating means adding resultstogether a vector including a component of the generated weighted vectoras a candidate of a quantized acoustic parameter with respect to theacoustic parameter in the current frame; a distortion computing part forcomputing a distortion of the quantized acoustic parameter with respectto the acoustic parameter calculated at the parameter calculating means;and a codebook search controlling part for determining the code vectorof the vector codebook and the set of the weighting coefficients of thecoefficient codebook by using a standard such that the distortionbecomes small, said codebook search controlling part outputting indexesrespectively representing the determined code vector and the set of theweighting coefficients as codes of the acoustic parameter.
 32. In thecoding device according to claim 31, wherein said vector codebookincludes a vector having a component of an acoustic parameter vectorshowing a substantially flat spectrum envelope.
 33. In the coding deviceaccording to claim 32, said vector codebook includes codebooks in pluralstages each storing a plurality of vectors in correspondence with anindex representing the vectors, and an adder for adding the vectorsoutputted from the codebooks in the plural stages to thereby output thecode vector, a codebook at one stage of the codebooks in the pluralstages stores said vector including the component of the acousticparameter vector showing the substantially flat spectrum envelope, andother codebooks at the other stages store a zero vector as one of thecode vectors.
 34. In the coding device according to claim 33, saidcodebook of at least one stage among the codebooks in the plural stagesis formed of a plurality of split vector codebooks for divisionallystoring a plurality of split vectors in which dimensions of the codevectors are divided in plural in correspondence with the indexrepresenting the split vectors, and an integrating part for integratingthe split vectors outputted from the plurality of the split vectorcodebooks to thereby output a result as an output vector of the codebookof the stage.
 35. In the coding device according to claim 32, saidvector codebook comprises: codebooks in plural stages each storing aplurality of code vectors in correspondence with an index representingthe vectors; scaling coefficient codebooks provided at respectivecodebooks on and after the second stage and storing scaling coefficientsdetermined in advance by corresponding to the respective code vectors ofthe codebook of the first stage in correspondence with an indexrepresenting the coefficients; multiplying means reading out acorresponding scaling coefficient from the scaling codebook with respectto the codebooks on and after the second stage, said multiplying meansmultiplying the code vector selected at the first stage with the codevector respectively selected from the codebooks on and after the secondstage, to thereby output multiplied results as vectors of the respectivestages; and an adder for adding vectors of the respective stagesoutputted from the multiplying means to the vector of the first stage,said adder outputting an added result as the code vector from the vectorcodebook; wherein a codebook of one stage of the codebooks in the pluralstages stores the vector including the component of the acousticparameter vector showing said substantially flat spectrum envelope, andcodebooks at the remaining stages store a zero vector.
 36. In the codingdevice according to claim 35, a codebook of at least one stage on andafter the second stage among said codebooks in the plural stages isformed of a plurality of split vector codebooks for divisionally storinga plurality of split vectors in which dimensions of the code vectors aredivided in plural, wherein said scaling coefficient codebookcorresponding to the codebook of said at least one stage comprises: aplurality of scaling coefficient codebooks for split vectors storing aplurality of scaling coefficients for split vectors, which are providedin plural to correspond to the plurality of the split vector codebooks,respectively in correspondence with the code vectors of the first stage;multiplying means for multiplying split vectors respectively outputtedfrom the plurality of split vector codebooks of said at least one stagerespectively with the scaling coefficient for split vectorscorresponding to the index of the vector selected at the codebook of thefirst stage by reading out said scaling coefficient from the respectivescaling coefficient codebooks for split vectors; and an integrating partfor integrating multiplied results to thereby output a result as anoutput vector of the codebook of the corresponding stage.
 37. In thecoding device according to claim 32, said vector codebook is formed of aplurality of split vector codebooks for divisionally storing a pluralityof split vectors in which dimensions of the code vectors are divided inplural, and an integrating part for integrating split vectors outputtedfrom the split vector codebooks and outputting a result as one codevector; and said vector including the component of the acousticparameter vector showing the substantially flat spectrum envelope isdivided into split vectors to be stored one by one as the split vectorsin the plurality of the split vector codebooks.
 38. The coding device ofclaim 34 or 32, wherein said vector codebook comprises: codebooks inplural stages each storing a plurality of code vectors in correspondencewith an index representing the vectors; scaling coefficient codebooksprovided with respect to the codebooks of the second and subsequentstages, respectively, and each storing scaling coefficientspredetermined for the respective code vectors of the codebook of thefirst stage in correspondence with indexes representing the scalingcoefficients; first multiplying means reading out scaling coefficientsfrom the scaling codebooks of the second and subsequent stages incorrespondence with the code vector selected from the codebook of thefirst stage, and multiplying the scaling coefficients with the codevectors selected from the codebooks of the second and subsequent stages,respectively, to thereby output multiplied results as vectors of thesecond and subsequent stages; and an adder for adding vectors of thesecond and subsequent stages outputted from the first multiplying meansto the vector of the first stage, said adder outputting an added resultas the code vector from the vector codebook; wherein a codebook of atleast one stage on or after the second stage among said codebooks in theplural stages is formed of a plurality of split vector codebooks fordivisionally storing a plurality of split vectors in which dimensions ofthe code vectors are divided in plural, wherein said scaling coefficientcodebook corresponding to the codebook of said at least one stagecomprises: a plurality of scaling coefficient codebooks for splitvectors storing a plurality of scaling coefficients for split vectors,which are provided in plural to correspond to the plurality of the splitvector codebooks, respectively in correspondence with the code vectorsof the first stage; second multiplying means for multiplying splitvectors respectively selected from the plurality of split vectorcodebooks of said at least one stage respectively with the scalingcoefficients for split vectors read out from said plurality of scalingcoefficient codebooks for split vectors corresponding to the index ofthe vector selected at the codebook of the first stage to producemultiplied split vectors; and an integrating part for integrating saidmultiplied split vectors to thereby output a result as an output vectorof the codebook of said at least one stage.
 39. An acoustic parameterdecoding device, comprising: a vector codebook for storing a pluralityof code vectors of an acoustic parameter equivalent to a linearpredictive coefficient showing a spectrum envelope characteristic of anacoustic signal in correspondence with an index representing the codevectors, a coefficient codebook for storing one or more sets ofweighting coefficients in correspondence with an index representing theweighting coefficients, and quantized parameter generating means foroutputting one code vector from the vector codebook in correspondencewith an index showing a code inputted for every frame, to thereby outputa set of weighting coefficients from said coefficient codebook, saidquantized parameter generating means multiplying the code vectoroutputted in a current frame and a code vector outputted in at least oneframe of the closest past respectively with the set of the weightingcoefficients outputted in the current frame, said quantized parametergenerating means adding multiplied results together to thereby generatea weighted vector, said quantized parameter generating means outputtinga vector including a component of the generated weighted vector as adecoded quantized acoustic parameter of the current frame.
 40. In thedecoding device according to claim 39, wherein said vector codebookstores a vector including a component of an acoustic parameter showing asubstantially flat spectrum envelope as one of the code vectors.
 41. Inthe decoding device according to claim 40, said vector codebook isformed of codebooks in plural stages each storing a plurality of vectorsin correspondence with an index representing the plurality of vectors,and an adder for adding the vectors outputted from the codebooks in theplural stages to thereby output a code vector, and a codebook at onestage of the codebook in the plural stages stores the vector includingthe component of the acoustic parameter vector showing the substantiallyflat spectrum envelope as one of the vectors, and codebooks at otherstages store a zero vector as one of the code vectors.
 42. In thedecoding device according to claim 41, a codebook of at least one stageamong said codebooks in the plural stages includes a plurality of splitvector codebooks for divisionally storing a plurality of split vectorsin which dimensions of the code vectors are divided in plural, and anintegrating part for integrating split vectors outputted from saidplurality of split vector codebooks to thereby output a result as anoutput vector of a codebook of a corresponding stage.
 43. In thedecoding device according to claim 40, said vector codebook comprises:codebooks in plural stages each storing a plurality of code vectors incorrespondence with an index representing the code vectors; scalingcodebooks each being provided with respect to respective codebooks onand after a second stage and storing scaling coefficients determined inadvance corresponding to code vectors of the codebook of a first stagein correspondence with an index representing the scaling coefficients;multiplying means for reading out a corresponding scaling coefficientfrom the scaling codebook with respect to the codebook on and after thesecond stage in correspondence to the code vector selected at the firststage, said multiplying means multiplying the code vectors respectivelyselected from the codebooks on and after the second stage with the readout scaling coefficient to thereby output multiplied results as vectorsof the respective stages; and an adder for adding the output vectors ofthe respective stages outputted from the multiplying means to the vectorat the first stage, to thereby output an added result as a code vectorfrom the vector codebook; wherein a codebook of one stage among thecodebooks in the plural stages stores said vector including thecomponent of the acoustic parameter vector showing the substantiallyflat spectrum envelope, and codebooks of the remaining stages store azero vector.
 44. In the decoding device according to claim 43, acodebook at least one stage on and after the second stage among thecodebooks in the plural stages is formed of a plurality of splitcodebooks for divisionally storing a plurality of split vectors in whichdimensions of code vectors are divided in plural, and said scalingcoefficient codebook corresponding to the codebook of said at least onestage comprises: a plurality of scaling coefficient codebooks for splitvectors storing scaling coefficients for a plurality of split vectorsprovided in plural corresponding to said plurality of split vectorcodebooks to respectively correspond to code vectors in the first stage;multiplying means for reading out scaling coefficients for split vectorscorresponding to an index of the vector selected at the codebook of thefirst stage from the respective scaling coefficient codebooks for thesplit vectors, said multiplying means respectively multiplying splitvectors respectively outputted from said plurality of split vectorcodebooks of said at least one stage with the scaling coefficients forsplit vectors; and an integrating part for integrating multipliedresults and outputting a result as an output vector of a codebook of acorresponding stage.
 45. In the decoding device according to claim 40,the vector codebook comprises a plurality of split vector codebooks forto divisionally storing a plurality of split vectors in which dimensionsof code vectors are divided in plural, and an integrating part forintegrating split vectors outputted from the split vector codebooks tothereby output a result as one code vector, wherein: the vectorincluding the component of said acoustic parameter vector showing saidsubstantially flat spectrum envelope is divided into split vectors eachbeing divisionally stored in each of said plurality of vector codebooks.46. The decoding device of claim 39 or 40, wherein said vector codebookcomprises: codebooks in plural stages each storing a plurality of codevectors in correspondence with an index representing the code vectors;scaling codebooks each being provided with respect to the codebooks ofthe second and subsequent stages, respectively, and each storing scalingcoefficients predetermined for the respective code vectors of thecodebook of a first stage in correspondence with indexes representingthe scaling coefficients; first multiplying means for reading outcorresponding scaling coefficient from the scaling codebooks withrespect to the codebooks of the second and subsequent stages incorrespondence to the code vector selected at the first stage, saidmultiplying means multiplying the code vectors respectively selectedfrom the codebooks of the second and subsequent stages with the read outscaling coefficients to thereby output multiplied results as vectors ofthe second and subsequent stages; and an adder for adding the outputvectors of the second and subsequent stages outputted from the firstmultiplying means to the vector at the first stage, to thereby output anadded result as a code vector from the vector codebook; wherein acodebook of at least one stage on or after the second stage among thecodebooks in the plural stages is formed of a plurality of splitcodebooks for divisionally storing a plurality of split vectors in whichdimensions of code vectors are divided in plural, and said scalingcoefficient codebook corresponding to the codebook of said at least onestage comprises: a plurality of scaling coefficient codebooks for splitvectors storing scaling coefficients for a plurality of split vectorsprovided in plural corresponding to said plurality of split vectorcodebooks to respectively correspond to code vectors in the first stage;second multiplying means for reading out scaling coefficients for splitvectors from the respective scaling coefficient codebooks for the splitvectors in correspondence with an index of the vector selected from thecodebook of the first stage, and multiplying split vectors respectivelyoutputted from said plurality of split vector codebooks of said at leastone stage with the scaling coefficients for split vectors; and anintegrating part for integrating multiplied results and outputting aresult as an output vector of a codebook of said at least one stage. 47.An acoustic signal coding device for encoding an input acoustic signal,comprising: means far encoding a spectrum characteristic of an inputacoustic signal by using the acoustic parameter coding method accordingto claim 2; an adaptive codebook for holding adaptive code vectorsshowing periodic components of said input acoustic signal therein; afixed codebook for storing a plurality of fixed vectors therein;filtering means for inputting as an excitation signal a sound sourcevector generated based on the adaptive code vector from the adaptivecodebook and the fixed vector from the fixed codebook, said filteringmeans synthesizing a synthesized acoustic signal by using a filtercoefficient based on said quantized acoustic parameter; and means fordetermining an adaptive code vector and a fixed code vector respectivelyselected from the adaptive codebook and the fixed codebook such that adistortion of the synthesized acoustic signal with respect to said inputacoustic signal to becomes small, said means outputting an adaptive codeand a fixed code respectively corresponding to the determined adaptivecode vector and the fixed vector.
 48. An acoustic signal transmissiondevice, comprising: an acoustic input device for converting an acousticsignal into an electric signal; an A/D converter for converting thesignal outputted from the acoustic input device into a digital signal;the acoustic signal decoding device according to claim 47 for encodingthe digital signal outputted from the A/D converter; an RF modulator forconducting a modulation process and the like with respect to encodedinformation outputted from the acoustic signal coding device; and atransmitting antenna for converting the signal outputted from the RFmodulator into a radio wave and transmitting the same.
 49. An acousticsignal receiving device, comprising: a receiving antenna for receiving areception radio wave; an RF demodulator for conducting a demodulationprocess of the signal received by the receiving antenna; the acousticsignal decoding device according to claim 27 for conducting a decodingprocess of information obtained by the RF demodulator; a D/A converterfor converting a digital acoustic signal decoded by the acoustic signaldecoding device; and an acoustic signal outputting device for convertingan electric signal outputted from the D/A converter into an acousticsignal.